ASSESSMENT OF NEUTROPHIL AGGREGATION BY COULTER(R) STKR AND STKS HEMATOLOGICAL ANALYZERS

We have studied an alternative method to aggregometry for the assessme nt of human polymorphonuclear (PMN) leucocyte aggregation. This simple , rapid and reliable procedure counts unaggregated cells on both Coult er(R) STKS and STKR haematological analysers by the impedance principl e. Aggregation of PMN was induced by 15 min incubation with fresh auto logous serum (FAS) after a 10 min phorbol myristate acetate (PMA) acti vation of neutrophils in small aliquots (0.25 ml) of suspension contai ning about 4.0 x 10(9) PMN/I. Differences (x100) between count of rest ing and PMA+FAS treated neutrophils/count of resting PMN reflect perce nt aggregation. By this procedure, PMN aggregation did not occur in au tologous plasma from EDTA anticoagulated whole blood; it was partially inhibited by hydrocortisone, whereas inactivated or Zymosan activated sera gave values similar to those from FAS induced aggregation. PMA a ggregation was dependent on Ca2+ + Mg2+ concentration. Intra-assay ana lytical variability did not exceed 4% on either instrument. Reference values (n=20) of percent PMN aggregation were 50.7 +/- 4.7 on STKS and 47.1 +/- 4.8 on STKR. Most probably, the interindividual variance was due to the physiological variability of Mg2+ and/or Ca2+ concentratio ns in FAS. Thus, this procedure reflects the true PMN aggregability st atus in a given subject, and in a given electrolyte environment.